The invention relates to a belt tensioner system.
Such belt tensioner systems are also known as so-called linear tensioners. They can be constructed as an end fitting tensioner or buckle tensioner. Furthermore, belt tensioner systems are known, in which the power transmission means engages on the belt between the end fitting and the deflection fitting arranged on the B-column and draws the belt downwards. The belt tensioner systems known hitherto have the disadvantage that they take up a large amount of space and that the elongated piston/cylinder unit generally projects vertically upwards from the vehicle floor. The known belt tensioner systems require a very large amount of space, so that their accommodation in the vehicle presents problems. Furthermore, the sealing of the traction cable, which forms the power transmission means, is a problem with respect to the end wall of the cylinder through which the traction cable extends. A good seal is only possible here with a high expenditure.
The invention provides a belt tensioner system which is small in size and is simply constructed, and which is distinguished by a high degree of variability of installation in the vehicle. This is achieved in a belt tensioner system which comprises a belt, a piston/cylinder unit comprised of a piston and a cylinder, and a drive for the piston/cylinder unit. The system further comprises a power transmission means which is directly connected with the piston/cylinder unit and, at least in the case of restraint, with the belt and which on activation of the drive converts a movement brought about in the piston/cylinder unit into a displacement of the belt. The power transmission means is constructed as a push rod. In contrast to the known tensioner systems, in which the power transmission means engages directly on the belt, in the belt tensioner system according to the invention, no traction cable is provided, but rather a push rod. The push rod can project out from the end of the cylinder opposite to the drive, the sealing taking place with respect to this free end of the cylinder through the seal of the piston. An additional sealing of the power transmission means with respect to the cylinder, as was necessary in the prior art between traction cable and end wall, is dispensed with.
The use of a push rod in connection with a belt deflection, when the belt is part of the system, provides for a small structural space for the belt tensioner system. The deflection of the belt is achieved through the push rod which defines the apex region of the deflected belt and displaces this apex region axially. The apex region does not have to be a fixed region of the belt, but rather is usually the region of the belt which is deflected. On displacement of the push rod, the section of the push rod which engages on the belt travels along the belt and displaces the apex region in axial direction. As the push rod is arranged as it were between the belt webbing sections which are deflected for example through 180xc2x0 and displaces the apex region, the belt webbing with a piston travel s is displaced by twice s, i.e. twice the distance. The piston/cylinder unit together with the drive system can therefore be of shorter and smaller construction with the same tensioning length than with a conventional linear tensioner which is to have the same tensioning length. The belt tensioner system is therefore also axially short in construction, because owing to the provision of a push rod, the piston/cylinder unit together with the drive lie between the deflected belt webbing sections, i.e. can be surrounded by the belt. With an arrangement of the piston/cylinder unit outside the space defined by the deflected regions, the axial structural space of the belt tensioner system is lengthened by the axial length of the piston/cylinder unit together with the drive connected therewith.
When the push rod has at its end remote from the piston/cylinder unit a curved belt contact surface engaging on the belt and defining the apex region, a lower-friction relative movement results between the contact surface and the belt. In addition, the contact surface must be constructed such that a sliding down of the belt from the contact surface during the tensioning process is prevented. In order to achieve this, the push rod has an elongated section running parallel to the displacement direction and a section adjoining the end of this elongated section on the webbing side, extending transversely hereto. This section running transversely to the elongated section has the curved belt contact surface.
The belt is deflected in a housing. The piston/cylinder unit together with the drive is constructed according to the preferred embodiment as a separate, preassembled module. This module can be transported independently of the housing and of the belt and can only be inserted into the housing at the end of the assembly procedure and arranged on it or on the vehicle. Thus, a type of modular concept results, which permits a so-called separate assembly of safety belt and tensioner drive (piston/cylinder unit with drive). In the prior art, usually complete units of safety belt and tensioner drive are necessary, which are bulky for assembly in the vehicle and are only able to be arrested with increased expenditure. In the belt tensioner system according to the invention, the belt can already be fully installed in the vehicle. Then, by fastening the pre-assembled module, the belt tensioner system is completed.
The belt runs in or immediately outside the housing through a deflection fitting and extends after the deflection fitting substantially transversely to the longitudinal axis of the cylinder. With this design, the belt tensioner system, which as a whole is elongated in construction, can be installed lying, i.e. horizontal and parallel to the vehicle floor. Its position can, however, be varied by the deflection fitting between the belt tensioner system and the belt running outside the belt tensioner system, without a different construction of the belt tensioner system being required.
The piston/cylinder unit is preferably fastened to the deflection fitting. This has the advantage that the piston/cylinder unit or the entire assembly of piston/cylinder unit with drive and the housing together with the belt deflected therein do not have to be fastened by means of separate openings in the vehicle. Fastening openings in the vehicle in fact have large tolerances with respect to each other. If, however, the piston/cylinder unit is fastened to the deflection fitting, these two parts can be produced in close tolerances in the region of their fastening, which simplifies the assembly. Furthermore, the piston/cylinder unit can of course also be arrested on the housing or on an end fitting. Here, the same advantages just mentioned result in assembly and manufacture.
In order to save overall height, which depends in particular on the diameter of the cylinder, instead of one piston/cylinder unit, also a plurality of units connected in parallel can be provided, which are coupled with each other. A further possibility of saving overall height consists in selecting an oval or rectangular cylinder.